The interim rule revises the clause to provide for contractor personnel other than private security contractor personnel to use deadly force against enemy armed forces only in self-defense. Private security contractor personnel are also authorized to use deadly force when necessary to execute their security mission to protect assets/persons, consistent with the mission statement contained in their contract.

So mercenaries are now "privateers". Like Jon Rogers says, everyone who wants to live in the 21st century, over here. Those of you who want to live in the 18th century, over there. Good luck with that.

The interim rule goes on to define the sorts of military operations private contractors can engage in:

Other military operations means a range of military force responses that can be projected to accomplish assigned tasks. Such operations may include one or a combination of the following: Civic action, humanitarian assistance, civil affairs, and other military activities to develop positive relationships with other countries; confidence building and other measures to reduce military tensions; military presence; activities to convey messages to adversaries; military deceptions and psychological operations; quarantines, blockades, and harassment operations; raids; intervention operations; armed conflict involving air, land, maritime, and strategic warfare operations; support for law enforcement authorities to counter international criminal activities (terrorism, narcotics trafficking, slavery, and piracy); support for law enforcement authorities to suppress domestic rebellion; and support for insurgency, counterinsurgency, and civil war in foreign countries.

Phew. They're only allowed to engage in civil war in foreign countries. Thank God. You know, I kind of think "armed conflict involving air, land, maritime and strategic warfare operations" covers kind of sort of EVERYTHING a para-military force would be allowed to do. As Steph pointed out, it doesn't cover driving an ice-cream truck, but everything else seems well-covered.